[PATCH] packet: Don't write vnet header beyond end of buffer

From: Benjamin Poirier
Date: Mon Aug 28 2017 - 14:30:05 EST


... which may happen with certain values of tp_reserve and maclen.

Fixes: 58d19b19cd99 ("packet: vnet_hdr support for tpacket_rcv")
Signed-off-by: Benjamin Poirier <bpoirier@xxxxxxxx>
Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
---
net/packet/af_packet.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 008a45ca3112..1c61af9af67d 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2191,6 +2191,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
struct timespec ts;
__u32 ts_status;
bool is_drop_n_account = false;
+ bool do_vnet = false;

/* struct tpacket{2,3}_hdr is aligned to a multiple of TPACKET_ALIGNMENT.
* We may add members to them until current aligned size without forcing
@@ -2241,8 +2242,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
netoff = TPACKET_ALIGN(po->tp_hdrlen +
(maclen < 16 ? 16 : maclen)) +
po->tp_reserve;
- if (po->has_vnet_hdr)
+ if (po->has_vnet_hdr) {
netoff += sizeof(struct virtio_net_hdr);
+ do_vnet = true;
+ }
macoff = netoff - maclen;
}
if (po->tp_version <= TPACKET_V2) {
@@ -2259,8 +2262,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
skb_set_owner_r(copy_skb, sk);
}
snaplen = po->rx_ring.frame_size - macoff;
- if ((int)snaplen < 0)
+ if ((int)snaplen < 0) {
snaplen = 0;
+ do_vnet = false;
+ }
}
} else if (unlikely(macoff + snaplen >
GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len)) {
@@ -2273,6 +2278,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
if (unlikely((int)snaplen < 0)) {
snaplen = 0;
macoff = GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len;
+ do_vnet = false;
}
}
spin_lock(&sk->sk_receive_queue.lock);
@@ -2298,7 +2304,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
}
spin_unlock(&sk->sk_receive_queue.lock);

- if (po->has_vnet_hdr) {
+ if (do_vnet) {
if (virtio_net_hdr_from_skb(skb, h.raw + macoff -
sizeof(struct virtio_net_hdr),
vio_le(), true)) {
--
2.14.1